loewe



S. LOEWE April 5, 1932.

HOT WIRE MEASURING INSTRUMENT Filed Jan. 20, 1930 2 Sheets-Sheet l v Jaw7f:

ApriI 5, 1932. s. LOEWE HOT WIRE MEASURING INSTRUMENT Filed Jan. 20,1930 2 Sheets-Sheet 2 .caused to a further object of my invention thePatented Apr. 5, 1932 UNITED STATES PATENTtOFFICE SIEGHUND LOEWE, OFBERLIN, GERMANY HOT WIRE IEASURmG-INSTRUMENT Application filed January20, 1930, Serial No. 428,211, and in Germany January 22,1929.

rect current and alternating current of any fre uency.

y invention consists of the combination of an electron valve with a hotwire which in known manner 'elongates or increases its deflectionaccording to the assing current to be measured. It may best e applied bythe position of one or several electrodes of an electron valve being inrelation to the other electrodes of the same amplifier system chan edunder the influence of the change in the s a e of a hot wire or similarconductor by the entry of current. According change will appropriatelybe eflected in such a manner that the change in the position of l theelectrode due to the heating of the hot wire produces a variation of theplate current of an electron valve which for this purpose is operatedwith constant'plate voltage source and grid bias.

By this method it is ossible to transform small variations of t throughthe hot wire into large variations of the plate current. A furtherincrease of the transformation may be eflt'ected by the plate circuit ofthe first electron valve being in known manner coupled with severalfurther electron valves, e. g. with a resistance amplifymg cascade whenminute variations of cur-' rent to be measured correspond toconsiderablevariations of current of the plate current of the terminal .valve. Thesevariations may be indicated in several known ways, for instanceacoustically,-or may be measured, for instance, by any galvanometer,possibly also by a less sensitive hot-wire instrument. If desired, anyrelay, too, which has to operate on a smaller current intensity, may beactuated by the terminal plate current circuit. 7

The control of the electrode position by the hot wire may be eflected bythe walls of the electrode valves being in some spots madeso e currentspassing manner that it is electrically independent thin that adeflection is possible. The change of position of the hot-wire outsidethe valve thus influences across the deflection of the glass bulb wallthe position of an electrode which is comparatively well connected withthis spot of the wall of the bulb, whilst the other electrodesare bestconnected with the other points of the bulb-wall (or the valve pedestal)and are therefore not exposed to p the relative changes of position.According to a further object of my in-. vention the hot-wire is sealedinto an electron valve and influences directly the position of anelectrode inside such a valve. The electrode may be influenced in such away that the position of the anode is changed whilst at the same timethe position of grid and cathode to one another remains constant. Inthis manner, as a rule, particularly good v results mag be obtained. Inaddition the V grid may e changed in its position to the anode andincandescent'filament or in the density of its mesh and the like. Bymoving the grid with respect to the incandescent wire speciallysensitive embodiments of the invention may be obtained.

Finally it is possible to influence the cathode in its position by meansof the hot-wire. The hot wire may be connected in such a from theconnection of the electron valve or so that one of the hot-wire leadscoincides with one of the electron leads, e. g. with the grid lead, orthat the two leads of the hot- Wlle coincide each with one lead of anelec- 5 trode, e. g. with the two cathode-leads. This may be efiected insuch a manner that by the heating of the hot-wire only the position ofthe cathode in relation to the other electrodes is changed, for instanceif cathodes are used the emission of which is independent or littledependent upon the temperature of the oathode, e. g. in the case ofphotoelectric emission or in such amanner that at the same time with theheating of the hot-"wire the'emission of the'cathode is increased sothat with a constant grid potential the corresponding plate currentfluctuates to a considera ole degree In order to increase thesensltivlty it may be useful to combine several of the abovementionedarrangements.

In order to obtain particularly handy and well useful hot-wiregalvanometers of high sensitivity, the wire to be heated may be arrangedin a multiple valve which simultaneously contains in known manner aresistance amplifying cascade (e. a triple valve). The further one ortwo eads necessary for this purpose do not cause any additionaldifiiculty in the construction of the multiple valve. By such anarrangement an apparatus is obtained in a single valve which reacts uponvery small current intensities with great changes of the output platecurrent.

' The valve is best constructed in such a manner that the fluctuationsof the plate current in the plate circuits, especially in the platecircuit of the terminal stage under the influence of the heating are aslarge as possible, while the feed current has not to be large.

, Therefore the grid bias could be adjusted in such a way that thesmallest plate currents to be expected are almost zero. If the measurinor indicating instrument to be connecte at the end, is not loaded withconsiderable feed currents, a higher sensitivity may be obtained in thecase of many arrangements (for instance if less sensitive hot wireinstruments are used in the output circuit). With such indicatinginstruments, however, like olarized relays in the output circuit, whichrequire a rectified current of fixed minimum current intensity andoperate on the fluctuations of such a current, the grid bias is adjustedso as to produce such 9. current in every instance.

It is known that the sensitivity of hot wire instruments may beincreased by the increase of the amplitude of movement of the hot wireby means of a (mechanical) lever transformation and by the subsequenttransmission of such amplitude to an indicator. The sensitivity isincreased to completely difl'erent orders of magnitude if such amechanical transformation for the increase of the amplitude of movementis first connected to a hot wire and if subsequently the position of theelectrode of an amplifier system is controlled with the amplitudes thusincreased, if thereb a further considerable increase of sensitivity isobtained and if finally by connection with a normal amplifier cascadethe current, thus changed, of the primary valve is regenerated.

In constructing the apparatus according to my invention provision shouldbe made against undesired heating of the hot wire from other sources.This is effected for instance in the cases in which for any reasonswhatsoever the heat supply b the heating would not be constant, by a termo-technic screening of the hot wire against the heat of theincandescent filament. It will be best to arrange the hot wire in suchpoints of the valve in which upon the short operation of the valve onthe one hand and upon a short heating of the hot wire on the other handa constant temperature is produced. For such 1purpose those valves aremost suitable the ulbs of which are either not at all or only in partprovided with a mirror-like coating. If the hot wire is considerablyheated it is advisable in this connection to arrange the hot wire closeto an uncoated point of the glass wall in order that the factors ofemission for the hot wire remain constant. If, however, the temperaturesof the hot wire to be expected, are so small that the heat discharged bythe hot wire does not noticeably influence the temperature of the valve,it will be advisable to arrange the hot wire opposite those points ofthe valve where by the coating of the walls it is protected from outsidedisturbances. In this case it may be particularly advisable to arrangethe incandescent filament, if any, of the valve close to an uncoatedpoint in order that the heat emitted by it may be rapidly and directlyradiated. It may finally'be expedient to give the coated part of theglass bulb such a shape as to effect that the part of the heat evolvedby the incandescent filament which is radiated against the coatedportions of the inner wall of the valve, after being once reflected bythe valve parts is directly thrown to the outside. This may be done bythe incandescent wire being arranged in the focus of a parabolically shaed coated head of the electron valve so t at the heating of theincandescent filament is prevented from influencing the heating of thehot wire.

The four figures represent exemplary forms of construction of myinvention.

Fig. 1 is a diagram of a circuit in which the valve which, according tomy invention, is controlled by a hot wire may be used in a connectionwhich results in a very great sensitivity.

Fig. 2 shows a valve in which the hot wire is arranged inside the samevalve which contains the electrode system to be controlled and in whichthe control of one electrode (the grid) is effected by a levertransmission.

Fig. 3 is an arrangement in which one cathode which, in both the coldand hot state, emits electrons, changes its position.

Fig. 4 shows an appropriate arrangement of the valve coating throughwhichrthe heat generated by the incandescent filament is thus reflectedto the outside of the valve, so that the hot wire is not influenced in adisturbing manner.

In Fig. 1, 1 is a discharge'vessel any one electrode of which iscontrolled in its position by the hot wire H being arranged in theinterior of the discharge vessel. The figure indicates by a dash-dotline 2 diagrammatically that the incandescent filament 3 is by the hotwire changed in its position in relaelectron valve 1 whose cathode tionto the other electrodes, but the circuit diagram of Fig. 1 is in othermanner useful for a different control of electrodes. In the 3 may, forinstance, be heated by means of a static current source, e. g.-by meansof the accumulator 4, the grid 5 and anode 6 in relation to the cathode3 may also lie at a constant and not fluctuating potential, for instancea plate battery 7. By a suitable connection, expediently by a resistanceamplification consisting of a plate-resistance 8, block condenser 9 andleak resistance 10, a further electron valve '11 is joined u in whoseplate circuit or in the plate circuit of a following stage coupled in asimilar manner any amm-eter 12 may be arranged which need not beparticularly sensitive. The hot wire H may be a thin wire compared withthe lead in wires 13 and 14 to which the electric factor (voltage andthe like) may be joined at M. In this arrangement the hot wire H isprotected against unevenly cooling influences by suitable ing devices, ascreen and the like.

If a current passes .through the wire H and if in consequence of theheatin the latter expands, it influences any one of the electrodes ofthe first valve 1. With constant grid bias the plate current of suchfirst valve thereupon changes. The variations are amplified by thefurther amplification stages with the result that the terminal stageshows protectwhich may be measured by a simple instrument.

Fig. 2 shows in a valve 1 a cylindrical electrode system consisting ofthe stretched incandescent wire 3, the spirally wound grid 5 and thecylindrical anode 6. Through the squash of the valve 1 two leads 13 and14' presses by its own gravity or, if necessary,

with the aid of the strain of a spiral spring 41 fastened'at the squashupon the lever 19, the right end of which is thereby pressed downward sothat its left end holds the hot wire H in tension. The hot wire extendsas soon as it is heated by the passage of a current supplied by means ofthe leads 13 and 14. Consequently the grid is pulled downward. Theamplification factor of the valve changes accordingly, so that even witha constant grid bias the plate current is fluctuating. With thearrangement according to Fig. 2 it is furthermore possible to use one ofthe' leads 13 or 14 simultaneously as a lead for the constant grid bias.

Fig. 3 shows diagrammatically an electron valve with flat plate 6, withzig-zag strained grid 5 and V-shape strained cathode 3 which rectionvertical to the l (indicated by a considerable variation of the platecurrent 'erated in it.

the right end changes its position corresponding to the heat expansionof the thread 3 by a spring 23, for example, stretching and strainingthe "cathode 3 towards the right whilst at the same end a'spring 24grips in the dilevel of the drawings and upon a change of position ofthe thread as a consequence of a heating draws the thread outside. thelevel of the drawings, i. e. away from the grid (or possibly nearer tothe grid).

The construction according to Fig. 3 may also beefiected such that thecathode 3 is arranged as a normal incandescent filament and thatcorresponding fluctuations of the emission current varied by thechanging temperatures of the hot wire are measured at the plate currentor for further amplification are led to an amplification cascade. Inthis arrangement it may be expedient in the interest of sensitivity,though not being always necessary, to provide a separate grid 5. Fig. 4shows diagrammatically a valve 1 the upper part of which has a mirrorcoating a double line). The mirrorcoated head is constructed as arotation paraboloid or a parabolic cylinder or the like in the focus ofwhich the incandescent filament 3 of the electrode system and the anode6 and grid 5 are arranged so that the heat evolved by the electrodesystem and especially-by the incandescent filament 3 is emitted outsidethe valve (cf. the dotted primary rays 26 and the reflected rays 27). hemirror coated portion'may' be given any other shape where a dispersal ofthe heat generated inside the valve is effected to the outside in'orderthat the hot wire H may not be noticeably influenced by the radiation.It may be expedient, moreover,'to arrange the level direction of the hotwire H warped to the direction of the elec rode system axis andparticularly to the direction of the incandescent filament 3. Or the hotwire may come to lie in the shadow of the plate cylinder 6, so that itneither reflects heat radiation nor obtains reflected heat radiationfrom the incandescent filament 3. If, as indicated in Fig. 4, it isoutside arranged in the neighbourhood of the uncoated portion of thebulb 1, it rapidly emits directly the heat gen- The apparatus then haslittle heat inertia. Therefore only a short starting time is necessarybefore the instruments indicate well and evenly.

A considerable heat inertia is preferred in many cases for thesuppression of undesired fluctuations in electron valves (e. g.

with thick short incandescent wires for the purpose of direct heatingfrom the mains the fluctuations of which shalt not appear inv the platecurrent). In contradistinction to this it is expedient for my inventionthat not only the hot wire, but the eiectrode system too should possesslittle heat inertia in order that the plate current may follow thefluctuations of the hot wire condition. For this purpose the hot wire inthe arrangement according to Fig. 3 as well as in the other forms ofconstruction is appropriately made very thin.

My invention is not limited to those measuring instruments by means ofwhich electric values are to be measured directly; it may with theappropriate changes be applied also in those cases in which otherfactors influence a hot wire and indicate its changes, e. g. in theoperation of a hot Wire in fire alarms and similar indicating devices.

I claim:

1. A measuring instrument with a hot wire and a system with severalelectrodes and means to influence the relative position of theelectrodes by the hot wire.

2. A measuring instrument with a hot wire and a system with severalelectrodes and means to influence the position of the cathode withrespect to the other electrodes by the hot wire.

3. In a hot wire measuring instrument a long thin filament andelectrodes neighboured to this filament and springs to avoid variationsof the distance of this filament to the further electrodes if thefilament is expanded by the heating.

4. In a hot wire measuring instrument a hot wire and an electrode systemand means to influence the amplification factor of the electrode systemby heating the hot wire.

5. A measuring instrument with a hot wire and a system with severalelectrodes and means to influence the relative position of theelectrodes by the hot wire arranged in a common vacuum bulb.

6. A measuring instrument with a. hot wire and a system with severalelectrodes and means to influence the relative position of theelectrodes by the hot wire together with amplifying systems arranged ina common vacuum bu- 7. A measuring instrument with a hot wire and asystem with several electrodes and means to influence the position ofthe cathode with respect to the other electrodes by the hot wire, thecathode having a coat emitting electrons when the temperature isslightly increased.

8. A measuring instrument with a hot wire and a system with severalelectrodes and means to influence the'position of the cathode withrespect to the other electrodes by the hot wire the cathode having aphoto-electric coat being influenced by a source of constant lightintensity.

signature.

SIEGMUND LOEWE.

